Preventing corrosion of ferrous metals



rnnvan'rmo ooaaosron or FE EMS signers,

Petersburg, Va, and

Process Company, New York, N. Y a core tionoi New York No Drawing. Application December 19, N36, Serial No. 116,711

1% Claims.

The present invention relates to methods of reducing corrosion of ferrous metals by ammonium nitrate solutions containing free ammonia.

In recent processes for the ammoniation of superphcsphates, use is-made of solutions containing large percentages of ammonium nitrate and also free ammonia. The provision of methods which reduce or prevent the corrosion. of apparatus in which these solutions are handled constitutes amajor problem in the commercial use oi these solutions, since, when ammonium nitrate-ammonia solutions, of the concentrations used, are shipped in tank cars of the usual construction, rapid corrosion occurs and the tank soon is not usable. Also corrosion occurs in apparatus'constructed of ferrous metal in which the solutions are handled.

It is an object of this invention to provide a method for reducing the rate of corrosion of ferrous metals by corrosive solutions of ammonium nitrate containing free ammonia, so that t is commercially practicable to employ apparatus of these metals for the storage and transportation of such solutions.

It is a further object of this invention to provide solutions of ammonium nitrate containing free ammonia which but slowly corrode ferrous metals.

According to the present invention, the apparatus which may be a storage tank, tank car, conveying pipe, measuring tank or the like, is constructed of the ferrous metals commonly used for this purpose, such as cast iron, wrought iron and low carbon steels, for example structural steel, which are subject to severe corrosion by ammoniacal solutions of ammonium nitrate. 1

According to'this invention, a material is added to the ammoniacal ammonium nitrate solution which reduces the rate of corrosion by such solutions of ferrous metals. These materials belong to the general class of compounds containing divalent sulfur linked to carbon. Of these compounds we preferably employ those in which there is a group of the type C-S -X in which X is the same carbon atom as C, is a different carbon atom from C, or is the compounds which are operative to reduce the rate of corrosion, the following are noted: carbon disulflde (S=C=S); the thio alcohols, such as ethyl mercaptan (C2H5.SH) and benzyl mercaptan CsHsCI-IzSI-I; the thio others, such as ethyl sulfide [(CzI-IslzSl; the organic thio acids, their salts and esters, for instance the thiocyanates', the thio analogues of carbonic acid, of the carboxyllc acids, and of the phenols such as ethyl hydrogen. As illustrative of (ill. 23-252) thiocyanate, the alkali metal thiocyanates (in cluding ammonium potassium xanthate thiacetic acid thiophenol CeHsSH, and thiobeta naphthol CIOH'ISH; the thiamides, for instance the thio analogues of the amides of carbonic acid and of the amides of the carboxylic acids, such as thiourea [(NH2)2C=S] and thiacetamide NHs respectively;

and heterocycllc compounds containing divalent sulphur in the ring such as thiophene and thiodiphenylamine The quantity of organic sulfur compound which may be incorporated to reduce rosion may vary from a very the rate of corsmall percentage upward. It is preferred, however, that the solution contain 0.004% to 0.8% calculated as sulfur.

of these materials More than 0.8% calculated purposes of the invention.

For example, any of the materials listed in the preceding paragraph may be added to a solution containing 60 parts of ammonium nitrate, 20 parts ammonia and 20 parts water which is contacted with low carbon steel in amount Accordingly, it is solution an amount corresponding to 0.04% sulfur. desirable to incorporate in the .of the sulfur compounds which is a minor proportion of the amount of the ammonium nitrate in the solution.

By the addition of a compound containing divalent sulphur linked to carbon,

the rate of corrosion of ferrous. metals by ammoniacal ammonium nitrate solutions is reduced to a very low rate.

This invention has specific application to aqueous solutions of ammonium nitrate containing free ammonia in which the ammonium nitrate constitutes about 50% or more of the solution (for example, 40% to 80%) and in which the ammonium nitrate is dissolved in 5% or stronger aqua ammonia, particularly in an aqua ammonia of about 25% or greater strength due to the relativelyhigh rates of corrosion exhibited by these solutions.

This invention also has specific application to contacting, at temperatures below about 50 C., ferrous metals with solutions containing ammonium nitrate and free ammonia, in which the sulfur compounds have been incorporated.

In order that this invention may be more clearly understood, the following examples typical of preferred methods of procedure are given by way of illustration: I

Example 1.0.08 part ethyl mercaptan is added to a solution containing 60 parts ammonium nitrate, 20 parts ammonia and 20 parts water.

This is equivalent to incorporating in the solution 0.04% ethyl mercaptan calculated as sulfur. The solution is then introduced into a container made of low carbon steel and cast iron and stored in such container at room temperature.

It has been found the presence of ethyl mercaptan reduces the rate of corrosion by the solution about 98.5%.

Example 2.-0.1l part ethyl sulfide (equivalent to 0.04% calculated as sulfur) is added to a solution containing 60 parts ammonium nitrate, 20 parts ammonia and 20 parts water. The solution may be introduced into apparatus constructed of low carbon steel and cast iron at room temperature.

It has been found the ethyl sulfide reduces the rate of corrosion about 98.5%.-

Example 3.0.09 part thioacetamide (equivalent to 0.04% calculated as sulfur) is added to a solution containing60 parts ammonium nitrate, 20 parts ammonia, and 20 parts water. The solution may be introduced into apparatus constructed of low carbon steel and cast iron at roomtemperature.

It has been found the thioacetamide reduces the rate of corrosion about 98.5%. I

Example 4.-0'.1 part thiacetic acid or 0.2 partthiobeta naphthol may be substituted for the ethyl mercaptan in Example 1. It has been found the rate of corrosion by the solution is reduced about 98.5% by such addition of either of these materials.

Example 5.0.l part thiophene may be substituted for the ethyl mercaptan in Example 1. It has been found the rate of corrosion by the solution is reduced about 97% by such addition.

The following theory is offered as a possible explanation of the effectiveness of the above processes for inhibiting corrosion of ferrous metals by ammoniacal ammonium nitrate solutions. It appears from our observations of the action of numerous salt solutions on ferrous metal that the chemical reaction which causes rapid corrosion of ferrous metals by ammoniacal ammonium nitrate solutions is peculiar to nitrate solutions and ferrous metals. Further, in the case of the nitrate solutions, rapid corrosion of the metal as a result of this reaction occurs only with the ammoniacal solutions. Thus, in the case of acid and neutral solutions of ammonium sion of the metal by the solution.

nitrate, hydrogen is evolved by the corrosion of ferrous metal by the solutions. In the case of corrosion by ammoniacal ammonium nitrate solutions, instead of detecting the evolution of hydrogen, we have observed that ammonia is formed by reactions taking place during corro- Under the conditions encountered in the corrosion of ferrous metals by ammoniacal ammonium nitrate. the presence in the solution of even a small amount of a sulfur compound of the type described appears to inhibit the particular type of corrosion there involved.

This application is in part a continuation of our co-pending application Serial No. 726,734, filed May 21, 1934.

In our copending application Serial No. 116,710, filed December 19, 1936, we are claiming specifically the process disclosed herein .of reducing corrosion of a ferrous metal by solutions of ammonium nitrate containing free ammonia by dissolving in the solution a compound containing divalent sulfur linked to an atom of carbon and the remaining valences of the carbon atom being satisfied by nitrogen and. more specifically, a thiocyanate or thiourea.

We claim: i

1. The process of reducing corrosion of ferrous metals by a solution of ammonium nitrate containing free ammonia, which comprises dissolving in said solution a compound containing divalent sulfur linked to carbon in amount sulficient to materially decrease the rate of corrosion of a ferrous metal by the solution, and contactmg said solution with said ferrous metal.

2. The process of reducing corrosion of ferrous metals by a solution containing about 50% or more ammonium nitrate dissolved in about 25% or stronger aqua ammonia, which comprises dissolving a compound containing divalent sulfur linked to carbon in said solution in amount suflicient to materially decrease therate of corrosion of a ferrous metal by the solution, and contacting said solution with said ferrous metal.

3. The process of reducing corrosion of ferrous metals by a solution of ammonium nitrate containing free ammonia, which comprises dissolving in said solution about 0.004 to 0.8%, calcumetals by a solution of ammonium nitrate containing free ammonia, which comprises dissolving in said solutionethyl sulfide in amountsufllcient to materially decrease the rate of corrosion of a ferrous metal by the solution, and contacting said solution with said ferrous metal.

6. The process of reducing corrosion of ferrous metals by a solution of ammonium nitrate containing free-ammonia, which comprises dissolving in said solution thiacetic acid in amount suflicient to materially decrease the rate of corrosion of a ferrous metal by the solution, and contacting said solution with said ferrous metal.

'7. As a new composition of matter suitable for storage, transportation and use in contact 11th ferrous metals, 8. solution containing free ammonla, ammonium nitrate and a compound containing divalent sulfur linked to carbon in amount sufiicient to materially decrease the rate of corrosion of a ferrous metal by the solution.

8. As a newcomposition of matter suitable for storage, transportation and use in contact with ferrous metals, a solution containing about 50% or more ammonium nitrate in solution inabout 25% or stronger aqua ammonia, in which is dissolved a compound containing divalent sulfur linked to carbon in 'amount suflicient to; materially decrease the rate of corrosion of a ferrous metal by the solution.

9. As a new composition of matter suitable for storage, transportation and use in contact with ferrous metals, a solution containing free ammonia, ammonium nitrate andethyl mercaptan in amount sufiicient to materially decrease the rate of corrosion of a ferrous metal by the solution.

10. As a new composition of matter suitable for storage, transportation and use in contactwith ferrous metals, a solution containing about 50% or more ammonium nitrate in solution in about or stronger aqua ammonia in which there is dissolved ethyl mercaptan in amount suflicient to materially decrease the rate of corrosion of a ferrous metal by the solution.

-11. As a new composition of matter suitable for storage, transportation and use in contact with ferrous metals, a solution containing free ammonia, ammonium nitrate and ethyl sulfide in amount suflicient to materially decrease the rate of corrosion of a ferrous metal by the solution.

12. As a new composition of matter suitable for storage, transportation and use in contact with ferrous metals, a solution containing about 50% or more ammonium nitrate in solution in about 25% or stronger aqua ammonia, in which there is dissolved ethyl sulfide in amount sufiicient to materially decrease the rate of corrosion of a ferrous metal by the solution.

13. As a new composition of matter suitable for storage, transportation and use in contact with ferrous metals, a solution containing free ammonia, ammonium nitrate and thiacetic acid in amount sufllcient to materially decrease the rate of corrosion of a ferrous metal by the solution.

14. As a new composition of matter suitable for storage, transportation and use in contact with ferrous metals, a solution containing about 50% or moreammonium nitrate in solution in about 25% or stronger aqua ammonia, in which there is dissolved thiacetic acid in amount sufllcient to materially decrease the rate of corrosion of a ferrous metal by the solution.

HIE-'Rll/[AIT A. BEEKHUIS, JR.

WILLIAM DE FOREST MACOMBER. 

